Printers, scanners, and so on are common office machines in the office. In order to enhance the convenience of use, an additional subsequence processing device, such as a stapler or a punch, is generally equipped with the office machines in recent years, so as to automatically process the sheets according to the requirement of the users before the sheets are outputted from the office machines. However, both of the stapler and the punch have various sizes for the sheet stacks with different thickness. If the sheets on the paper tray are thicker than a processing limitation of the stapler or the punch, not only the sheets but also the subsequence processing device may be damaged. Thus, a sheet stack thickness estimating device is usually equipped for ensuring the thickness of the sheets on the paper tray is lower than a presetting thickness to avoid the above mentioned damages.
FIG. 1A illustrates a schematic view of a conventional sheet stack thickness estimating device disclosed in the U.S. Pat. No. 6,773,004. The sheet stack thickness estimating device 1 in FIG. 1A comprises a driving device 11, a first connecting rod 12, a second connecting rod 13, a shaft 14, a pressing part 15, an elastic component 16 and a sensor 17. The first connecting rod 12 connects to the driving device 11. The second connecting rod 13 comprises a front portion 131, a middle portion 132 and an end portion 133. Here, the front portion 131 and the end portion 133 are respectively perpendicular to the middle portion 132, the front end 131 connects to the first connecting rod 12 and is pivoted to the shaft 14, and the shaft 14 is disposed on a frame 18. The pressing part 15 connects to the end portion 133 of the second connecting rod 13. The elastic component 16 connects between the frame 18 and the second connecting rod 13. The sensor 17 is disposed above the middle portion 132 of the second connecting rod 13.
Also referring to FIG. 1A, when the front edge of the sheet S is entering towards the paper tray 19, the driving device 11 drives the first connecting rod 12 to move towards the driving device 11 horizontally. Hence, the first connecting rod 12 pulls the front portion 131 of the second connecting rod 13, so as to drive the second connecting rod 13 rotates about the shaft 14 in the counterclockwise direction, and thus the second connecting rod 13 is raised to a first position (as the dashed line illustrated in FIG. 1A). At this time, the pressing part 15 is distant from the paper tray 19.
After whole of the sheet S enters into the paper tray 19, the driving device 11 stops to drive the first connecting rod 12 to move. Hence, the first connecting rod 12 stops to pull the front portion 131 of the second connecting rod 13, and thus the second connecting rod 13 is driven by a return force provided by the elastic component 16 to rotate about the shaft 14 in the clockwise direction until the second connecting rod 13 is lowered to a second position (as the continuous line illustrated in FIG. 1A) to let the pressing part 15 lean against the sheets S on the paper tray 19. At the same time, the second connecting rod 13 also pulls the first connecting rod 12 to move back towards the driving device 11 horizontally. As shown in FIG. 1A, after a stack of sheets S need to be processed are all entered into the paper tray 19 and the thickness thereof is lower than a presetting thickness, the middle portion 132 of the second connecting rod 13 does not interrupt the sensor 17, and then the controller la controls the subsequence processing device (not shown), such as a stapler or a punch, to bind or to punch the stack of sheets S.
FIG. 1B illustrates a side view of the conventional sheet stack thickness estimating device where a stack of sheets are entered into the paper tray thereof. Referring to FIG. 1B hereinafter, after a stack of sheets S need to be processed are all entered into the paper tray 19 and the thickness thereof is thicker than the presetting thickness, the middle portion 132 of the second connecting rod 13 interrupts the sensor 17, and then the controller 1a determines to stop binding or punching the stack of sheets S by the subsequence processing device (not shown), such as a stapler or a punch.
Accordingly, the sheet stack thickness estimating device 1 may detect whether the thickness of a stack of sheets S on the paper tray 19 is lower than the presetting thickness or not by the driving device 11, the first connecting rod 12, the second connecting rod 13, the pressing part 15 and the sensor 17.
However, the conventional sheet stack thickness estimating device 1 has problems as below. As described above, the sensor 17 must be disposed on the frame of the office machine above the sheet stack thickness estimating device 1. Therefore, the sheet stack thickness estimating device 1 is not only difficult to be modulized and utilized in the office machines with various sizes, but also requiring larger vertical installation space. Further, the sensor 17 must be distant from the shaft 14 for increasing a detectable range of the sheet stack thickness, and thus requiring larger horizontal installation space as well. In addition, the probability of generating an interruption signal before the sensor 17 being completely interrupted by the second connecting rod 13 is increased due to the moving direction of the second connecting rod 13 is perpendicular to the sensor 17, and thus it is likely to result in a misjudgement by the sheet stack thickness estimating device 1.
Accordingly, it is necessary to provide a novel sheet stack thickness estimating device to overcome the above mentioned problems of the conventional stack thickness estimating device.